1. Field of the Invention
The present invention relates to an electromagnetic flowmeter which applies a magnetic field to a fluid to be measured and picks up an electromotive force generated according to a flow rate of the fluid to be measured, and a production method thereof.
2. Description of the Related Art
Related art of electromagnetic flowmeters are normally classified into two groups, i.e., one having a couple of electrodes which have been left cut by a lathe or fine cutter and another having a couple of electrodes which have been cut by a lathe or fine cutter and then mechanically polished (substrate adjustment) with a grinding paper, buff or the like.
Such an electromagnetic flowmeter is arranged to allow the electrodes to pick up an electromotive force generated according to the flow rate of a fluid to be measured when a magnetic field is applied to the fluid (not shown). The electrodes of the electromagnetic flowmeter are adapted to pick up an electromotive force.
An electromagnetic flowmeter generates a flow noise when electric charge moves between the surface of the electrodes and the fluid to be measured. It is also known that when the electrodes of an electromagnetic flowmeter are soaked in a fluid to be measured (e.g., water) for a long period of time, the flow noise reduces.
The term “flow noise” as used herein is meant to indicate a noise generated when the fluid to be measured rubs against the lined surface (electrode), i.e., noise generated by electric charge with the movement of a fluid to be measured, remarkably a fluid having a low electrical conductivity and a low viscosity such as alcohol and pure water. In some detail, the flow noise falls when the dynamic viscosity or electrical conductivity of the fluid to be measured rises but rises when the flow rate of the fluid to be measured rises.
Specific flow noise characteristics will be described hereinafter in connection with FIGS. 4 to 6. In these figures, the abscissa indicates the time during which the fluid to be measured flows through the measuring tube of the electromagnetic flowmeter (since the time at which the measuring tube comes in contact with the fluid) and the ordinate indicates the magnitude of flow noise. In these figures, B-1 to B-9, C-1 to C-3 and D-1 to D-3 each indicate the measurements of the respective sample that are dispersed by the difference in properties between electrodes.
FIG. 4 illustrates the flow noise characteristics of a related art electromagnetic flowmeter wherein there is provided a couple of electrodes which have been left as it is lathed.
As can be seen in the characteristics of FIG. 4, the flow noise maintains a high level after the contact of the fluid with the measuring tube of the electromagnetic flowmeter and, even after several hours, doesn't readily fall and is much dispersed.
FIG. 5 illustrates the flow noise characteristics of a related art electromagnetic flowmeter wherein there is provided a couple of electrodes which have been lathed and buffed to smoothen the surface of the substrate.
As can be seen in the characteristics of FIG. 5, the flow noise is large after the contact of the fluid with the measuring tube of the electromagnetic flowmeter, but falls after the lapse of time.
FIG. 6 illustrates the flow noise characteristics of a related art electromagnetic flowmeter wherein there is provided a couple of electrodes which have been lathed and forcedly oxidized in the atmosphere.
As can be seen in the characteristics of FIG. 6, the flow noise is large after the contact of the fluid with the measuring tube of the electromagnetic flowmeter, but falls after the lapse of time. The flow noise in the characteristics of FIG. 6 is larger than that of FIG. 5.
The aforementioned related art of the production method an electromagnetic flowmeter has a step of assembling a couple of electrodes in a measuring tube (product assembly), a step of soaking the electrodes in a fluid to be measured for a predetermined period of time, and a step of correcting the electromagnetic flowmeter.
If the electromagnetic flowmeter has failed in the correcting step, a step of soaking the electrodes again in the fluid to be measured is then executed. Subsequently, a step of correcting the electromagnetic flowmeter is executed.
Some related art of electromagnetic flowmeters has a couple of oxidized electrodes (see, e.g., the following document (1).).
(1) Keisuke Kihara, et al., “Electrode Behavior of Electromagnetic Flowmeter”, Oct. 27, 28 and 29, 1993, 36th Proceedings of the Japan Joint Automatic Control Conference, 4,028 pp. 415
However, the electromagnetic flowmeters of the related art generate much flow noise shortly after coming in contact with a fluid. Further, the generated flow noise doesn't readily fall even after the lapse of time from the contact with the fluid. Further, the generated flow noise is much dispersed by the difference in properties between electrodes.
Further, the step of soaking the electrodes of the electromagnetic flowmeter in the fluid to be measured and the step of correcting the electromagnetic flowmeter require much time, it takes long time to produce the electromagnetic flowmeter.